1. Field of the Invention
The present invention relates to improvement on an image forming apparatus that is capable of forming wide images.
2. Background Art
An image bar used for wide exposure so as to form wide images, such as A0 size or A1 size, is not general and thus its device is very expensive. Consequently, some techniques have been proposed to arrange a plurality of A3 or A4 size image bars, which are generally used, to conduct the wide exposure.
For example, JP-A-6-258727 discloses an apparatus that is capable of conducting an exposure on a photoconductor in a direct line by arranging a plurality of image bars included in a liquid crystal structure.
Also, JP-A-6-255175 discloses an example of a plurality of LED (light-emitting diode) heads arranged in a zigzag pattern.
However, the above-mentioned techniques according to the related arts, it is difficult to determine with a high precision the positional relationship of the overlapping portions of the image bars or LED heads arranged in a zigzag pattern, i.e., the dots formed at the end portions in each of the image bars or the LED heads. In such case, if the dots at the end portions are overlapped with each other, black streaks appear in the printed images. If the dots at the end portions are deviated and thus gaps exist between them, white streaks appear on the printed images.
Furthermore, in CAD (computer aided design) drawings, the original dimensions of the drawn objects are often required to be maintained in the drawings. However, the resolution of the LED is generally denoted as the number of dots per inch (dpi). Meanwhile, since the meter system has been used as the unit in Japan when the LED heads are manufactured, there are problems that dimensional errors may occur as much as the fractional number generated at the time of unit conversion. The dimensional errors become conspicuous as the size of the LED heads become larger. Also, a paper may be shrunk by heating the paper when fixing the toner images on the paper and the shrunk paper may cause the dimensional errors, which is also problematic.